Polar Molecules
I. VSEPR Theory Review: Shapes of Molecules
States that electron pairs in molecules repel each other, and, "angularly" stay as far apart as possible around a central atom.
Shapes of molecules are determined by the number of bonds and lone pairs of electrons around a central atom.
Shapes of molecules will help us determine if a molecule is polar or nonpolar.
II. Polar Molecules
A. General Facts/Definition
Polar molecules are also called "dipoles."
Polar molecules have one end that has a partial negative ("delta negative") charge and one end with a partial positive ("delta positive") charge.
The atom(s) with the highest electronegativity have a partial negative charge because a high electronegativity means that the atom is an "electron hog."
The water molecule is a polar molecule. The oxygen atom is most electronegative.
B. Exactly how can I classify a molecule as polar?
Polar molecules as three-dimensionally "asymmetrical." This means that any molecule that has a central atom with two different types of elements connected to it is probably polar, because each atom has a different electronegativity.
Bent and trigonal pyramidal molecules are always polar. The lone pair(s) on the central atom automatically make the molecule asymmetrical around the central atom.
C. What common polar molecules should I memorize?
1. Water! Water is a bent molecule!
2. Ammonia! NH3 is a very common polar molecule!
3. Any bent or trigonal pyramidal molecule is polar!
4. Any nonsymmetrical molecular is polar!
